Epicentral distribution of the relocated hypocenters in the Izu-Honshu collision zone. Colors of circles signify the depth of hypocenters. The focal mechanisms of the earthquakes with magnitudes greater than 3.0 are also shown in lower hemisphere projections. The thin black lines indicate surface traces of active faults (Research Group for Active Faults of Japan, 1991). Rectangles A–B, C–D, and E–F correspond to the depth sections indicated in Fig. 3. The red broken lines indicate the depth contours of the conversion plane obtained by the inversion of arrival time data of S-P converted waves (Tsumura et al., 1993).